DE2705818A1 - METHOD FOR CATALYTIC REDUCTION OF NITROGEN OXIDE - Google Patents

Description

New England Power Service Company, Westborough (Mass.) »V.St.A. Process for the catalytic reduction of nitrogen oxide

Nitrogen oxides, especially nitrogen oxide, NO, are unwanted reaction products that arise when burning carbonaceous fuels, for example in power plants.

Various techniques have been suggested for removing nitrogen oxides from gas streams to avoid contaminating the atmosphere, such as absorption, Washing and catalytic conversion.

So became the catalytic reduction of nitrogen oxides with ammonia or hydrogen in the presence of nickel and iron and chromium oxides (US-FS 2,381,696; US-FS 3,008,796; DT-AS 1 259 298). The reaction is exothermic and the temperature in the catalyst bed controlled is difficult so that the ammonia burns easily.

O65- (657 54I) -TP

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The removal of nitrogen oxides from waste gas streams from nitric acid factories was achieved by reaction with ammonia, Hydrogen or Methane Over a supported platinum group metal catalyst performed (Anderson et al "Ind. Eng. Chem." Vol. 53, P. 199 (I96I); Adlhart et al "Chem. Eng. Progra". Vol. 67, Pp. 73-78 (1971)). With this method there was a difficulty in controlling the exothermic reaction that led to it Pressure shock waves and overheating of the reactor leads. Even In some cases, hydrogen cyanide is formed as a by-product.

In the case of power plant emissions, the exhaust gas typically contains as Main source of pollution is sulfur oxides or sulfur dioxide and nitrogen oxides. It has been found possible to separate the sulfur dioxide from the exhaust gas and separate the sulfur dioxide to treat. This results in a mainly sulfur dioxide with less than 2000 ppm, nitrogen oxide, oxygen, Exhaust gas containing nitrogen and water vapor.

The known method for the catalytic reduction of Nitrogen oxide with ammonia as the reducing gas give rise to problems with the operating temperature required to achieve the Maintain efficiency of the catalyst used, deterioration of the catalyst, control exothermic Reacts and prevents the formation of by-products that are polluting, especially nitrogen oxydul.

The use of a base metal catalyst to reduce nitrogen oxide to nitrogen with ammonia in

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the presence of oxygen and sulfur dioxide has already been indicated in DT-AS 1 259 2982, however, is the Catalyst life is limited and controls are not provided to prevent the formation of nitric oxide and the reaction is exothermic difficult to control. Next, in similar constituent systems, nitric oxide reduction was used to nitrogen with ammonia, the use of a copper-activated catalyst on a catalyst support such as alumina, silica or diatomaceous earth stimulated US Pat. No. 3,008,796. The reaction rates are not such that such a process is economically feasible for the treatment of a gas stream, such as B. from a power plant emission could be viewed. The elimination or prevention of the formation of undesirable by-products is not regulated.

The invention is based on the object of a method for the catalytic reduction of nitrogen oxide to develop nitrogen with ammonia as a reducing agent, with which a high percentage conversion of the Nitrogen oxide to nitrogen with ammonia while avoiding or keeping the formation of undesirable by-products such. B. nitrogen oxide «is possible.

Subject matter of the invention, which solves this problem is a process for the catalytic reduction of nitrogen oxide by contacting it with a catalyst on a metal basis in the presence of ammonia and oxygen and reduction of the nitrogen oxide to nitrogen, with the

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270581a - * -

Identifies that from the group of copper, vanadium, iron, chromium, nickel, molybdenum, cobalt, lanthanides and actinides or combinations thereof, selected basic catalyst of a pretreatment by contacting with a compound of the Group selenium, sulfur and sulfur compounds is subjected to that one nitrogen oxide, oxygen and Carbon dioxide-containing gas stream admixes ammonia and that the gas stream mixed with ammonia when avoided the formation of nitrogen oxide is brought into contact with the pretreated catalyst.

According to a preferred exemplary embodiment of the invention the base metal catalysts copper, vanadium and iron either alone or any combinations thereof pretreated with a sulfur compound and / or selenium. The pretreated catalyst is then used Reduction of nitrogen oxide to nitrogen in a multi-component system of ammonia, oxygen and a inert gas used.

With the catalytic! Reduction of nitrogen oxide too Nitrogen run in a multicomponent system of nitrogen oxide, oxygen, ammonia, and an inert gas probably several reactions. The more important reactions are:

6NO + 4NH ₅ > 5N ₂ + 6H ₂ O

16N0 + 4NH, > 10N ₂ O + 6H ₂ O

> 2N ₂ + 6H ₂ O

4O ₂ + 4NH ₅ > 2N ₂ O + 6H ₃ O

5O ₂ + 4NH ₅ > 4N0 + 6H ₂ ⁰

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In a system of nitrogen oxide and oxygen with ammonia to reduce the nitrogen oxide with or without When a noble metal catalyst is used, sulfur dioxide is added to both nitrogen and nitrogen oxide educated.

In a system of nitric oxide, oxygen and one controlled amount of sulfur dioxide is used when using a base metal catalyst the nitrogen oxide without substantial nitric oxide formation reduced to nitrogen. Where the amount of sulfur dioxide in the system is unknown, i.e. either no sulfur dioxide is present or no controlled one If the amount of sulfur dioxide is present, both nitrogen and nitric oxide are formed.

According to the invention, base metal catalysts are pretreated, and in the case of a system of nitrogen oxide and oxygen with ammonia, the pretreated catalyst is used Base metal catalyst formed essentially no nitrogen oxide. This pretreatment eliminates the need to control the amount of sulfur dioxide, if any Present in the system to avoid the undesirable by-product nitric oxide when using nitric oxide Ammonia is reduced to nitrogen using the pretreated base metal catalyst.

The method of the invention essentially comprises the pretreatment of a base metal catalyst from the group consisting essentially of iron oxides, vanadium oxides and copper oxides by contacting the catalysts with a pretreatment stream, which is an evaporable Sulfur compound, such as. B. dimethyl sulfide, hydrogen sulfide, sulfur dioxide, carbon disulfide or contains elemental sulfur, or selenium, to impregnate the catalyst. Ammonia becomes a nitric oxide and

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Oxygen-containing gas stream admixed to form a mixed Oasstroms which contacts the pretreated catalyst. The nitric oxide is reduced to nitrogen without substantial nitric oxide formation. To promote the formation of metal sulfides on the catalyst or the deposition of sulfur, the pretreatment gas stream preferably contains H ₂ or NH-. The pretreatment step is preferably carried out at temperatures between about 204.4 and 482.2 ⁰ C. The pretreatment or exposure time depends on the temperatures used and is generally between about 2 and about 24 hours, preferably 2 to 10 hours, the shorter time being applicable to the higher temperatures. The proportion of the vaporizable sulfur or selenium compound in the pretreatment gas stream can be 0.5 to 10 %, preferably 1 to 2 % .

The single figure shows a process scheme of the preferred exemplary embodiment according to the invention.

One recognizes a power plant 10 of 800 MW, which approximated a waste gas stream at between about 93 and # 3 537.8 ⁰ C, preferably from 148.9 to 371 * 1 ⁰ C, for example at 260 ⁰ C and with a throughput of 5 , Emits 6 χ 10 m / h. A typical composition of the exhaust gas is given in Table I below, it being understood that the composition may vary depending on the operating conditions and the type of fuel consumed.

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- 40- 2705818 Table I. Composition Vol. G of the exhaust gas component 1 ^, 5 kg / h CO ₂ 3.0 0.686 χ 10 ⁶ ° 2 0.2 1.032 χ 10 ⁵ so ₂ 0.075 1.378 10 ⁴ NO _x 0.2 2.417 x 10 ⁵ Fly ash from N ₂ and H ₂ O. The rest exists

The gas stream is discharged from power plant 10 with the above composition and introduced into a separator 12, where approximately 95 % of the fly ash is separated. The gas stream is discharged from separator 12 without the removed fly ash, and ammonia from a supply 14 is added as a reducing gas to the gas stream to form a mixed stream. This rented gas stream flows to a manifold 16 where it is introduced into a catalytic reactor 20 through a plurality of inlets 18a-d. The ammonia flow rate depends on the ammonia / nitrogen oxide ratio. For this example, Table II lists a range of molar ratios and the associated amount of ammonia available for the subsequent catalytic reaction.

Table II NH ^ / NO molar ratio kg NH, / h

0.7 959.6

0.8 1096.7

0.9 1233.7

1.0 1370.8

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The catalytic reactor 20 includes a plurality of Catalytic beds 22a-d. The gas streams introduced pass through the catalytic beds, where mainly the following Reaction is running.

6NO + 4NH-,

6H ₂ O

The catalyst volume depends on the space velocity. Table III gives the cubic meter requirements of the catalyst bed in relation to space velocity.

Table III

Room speed h ~ reactor conditions

25,000 50,000 75,000

100,000

Catalyst vol., Ur

2.372 1.186 0.791 0.593

The catalyst used in this particular embodiment is 10 % ^v p ° 5 ^on aluminum oxide, as available from Harshaw Chemical and designated V0301, which catalyst was pretreated. The percentage reduction in nitrogen oxide in the mixed gas stream under the conditions given here exceeds 80 % and can approach 100 % without formation of nitrogen oxide. A typical one from the catalytic reactor 20 through the outlets 24a-d and the manifold

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Composition delivered is reported in Table IV.

Table IV

according to the composition of the reactor exhaust gas / electrostatic

Deposition Part of Vol. K,

CO ₂ 14.5

O ₂ 2.9

SO ₂ 0.2

N0 _v 0.020

Fly ash 0.01

This reduced gas stream at between approximately 148.9 and 371 * 1 ^° C., for example 260 ^° C., is introduced into a heat exchanger 28, where it is cooled to approximately 176.7 ° C. by the air flowing in. It is then discharged to the chimney by means of a conventional fan 30.

The V ₂ Oc on alumina is pretreated to ensure that essentially no nitrogen oxide is formed, whether or not sulfur dioxide is present in the gas stream. The catalyst is, while contacted with a gas stream of 2% Dlmethylsulfid and 2% hydrogen in helium at a temperature of between about 260 and 371 * 1 ° C, for example 315.6 ⁰ C between about 4 and 8 hours, for example 6 hours. After the pretreatment, the catalyst is placed on supports for beds 22a-d.

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Other base metal catalysts that can be pretreated in the same way are copper, iron, chromium, Nickel, molybdenum, cobalt or suitable combinations thereof, usually based on a material of high specificity Surface, such as B. alumina, silica-alumina or zeolites, during pretreatment of the catalyst include other suitable compounds that can be used, hydrogen sulfide, sulfur

material
Oxide, carbon disulfide or elemental sulfur, or selenium under similar working conditions as those specified above.

In an alternative embodiment, the invention can be used to eliminate NO from the exhaust gas of a turbine generator, using a system that is functionally equivalent to that shown in the drawing. A turbine generator with an output of about 20 MW emits exhaust gas in an amount of about 85,000 ir per hour. A typical composition of the exhaust gas is given in Table V, the composition of course varying depending on the working conditions and the type of fuel used.

Table V

Composition of the exhaust gas Part Volume Part kg / h

0
2 0.16 7.45 x 10 ^{6 SO} x 28 χ 10 " ⁶ 26th NO 114 χ 10 " ⁶ 48.8 CO 5x10 " ⁶ 2

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The gas stream of the above composition given off by the generator is introduced into a catalytic reactor essentially in the same way as the type shown in the drawing and described in the previous exemplary embodiment. In particular, the catalytic reactor contains a plurality of catalytic beds in a columnar arrangement, which are accommodated in a plurality of zones. A reducing gas, in particular Amaoniak is admixed to the exhaust gas flow and thus introduced together through a manifold into the catalytic reactor at a temperature of between about 260 and 482.2 ⁰ C, for example 426.7 ⁰ C. The ammonia to nitric oxide molar ratio can vary from 0.7 to 1.0. The following table VI lists the molar ratios and the amount of ammonia required for the subsequent catalytic reaction.

Table VI kg NH, / h 19.38 NH3 / NO y 22.14 Mole ratio 24.92 0.7 27.68 0.8 0.9 1.0

The total catalyst volume depends on the space velocity. The following Table VII gives the cubic meter requirements of the catalyst in relation to space velocity which varies between about 25,000 hours "and 100,000 hours" ¹ .

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Table VII Catalyst volume Space velocity h ~ m ⁵ Reactor conditions 35.6 25,000 17.8 50,000 11.8 75,000 8.9 100,000

The catalyst used in this alternative embodiment is V ₃ O ₁ - with an aluminum oxide carrier, which is pretreated as in the preferred embodiment. The percent reduction in nitric oxide under the conditions given here is essentially 100 % with no substantial nitric oxide formation. A typical gas composition emitted from the catalytic reactor is given in Table VIII.

Table VIII

Composition of the reactor gas Component Volume fraction

SO _x 28 χ 10 " ⁶

0.15

10 " ⁶

NO 50 x 10

CO 5 χ 10 " ⁶

The following examples illustrate the suitability of the catalyst composition when used in the invention Procedure.

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example 1

Samples of six commercially available catalysts were used as supplied to break down nitric oxide Reduce ammonia in the absence of sulfur dioxide, and are given in Table IX.

Table IX

Catalyst type p

10 % CuO on aluminum oxide Cr-activated iron oxide copper chromite

3 % Pt on alumina

on
10 5 ^ V ₂ O ₅ / alumina

Manufacturer description Harshaw Cu0803 Girdler G3A Girdler 013 Matthey Bishop MB30 Harshaw TOOl Harshaw V0701

10 % V ₂ O ₅

Approximately 3 grams of each catalyst was charged into individual 6.35 mm diameter aluminum reactors and placed in an oven such as a Lindberg high efficiency oven. A gas mixture with approximately 520 ppm NH, 600 ppm NO, 5000 ppm O ₂ and the remainder He was over these catalysts with a space velocity of 38O hours. cc / gm-min headed. The results are given in Table X.

When compared to the inlet NO level, it can be seen that significant amounts of NO have been converted, however, that the majority of it was converted to NpO, an undesirable by-product, rather than to Np, the desired product.

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The catalysts of Example 1 were tested in a similar manner, except that approximately 2000 ppm sulfur dioxide was added to the oas mixture of Example 1. The results obtained are shown in Table XI. It can be seen from this table that the addition of sulfur dioxide to the gas mixture in the case of the base metal catalysts _{reduced the undesired formation of N 2} O to 0, Np being the only reaction product in these cases. However, the addition of sulfur dioxide did not prevent the formation of N ₃ O in the case of the platinum catalyst.

Table X Catalyst type

3 % Pt on alumina

3 % Pt " ^M

3 % Pt ""

3 % Pt ""

10 % CuO ""

10 % CuO ""

10 % CuO ""

10 % CuO ""

Copper chromite

Cr-activated iron oxide

10 %
10 %
10 %
10 %
10 %
10 %
10 %

10 %

V ₂ O ₅ on aluminum oxide V ₂ O ₅ ""

V ₃ O ₅ ""

V ₂ O ₅ ""

V ₂ O ₅ on SiO ₂ -Al ₂ O ₅ V ₂ O ₅ "" ⁿ

VO "" "

Temperature, ⁰ C

221.7 236.2 263.4

291.7

221.1

236.2

264

291.1

221.1

236.7

264

291.7

222.8

237.8

265.1

292.8

222.2

237.3 264.5 292.8 222.8 237.8 264.5

PPM product ^ ueaenen-

NO N ₂ O

11 10 46 79 79 81

II9 139 I8I 149 I87 258 175 203 219 220 44 59 70

222 220 140 83

^19T

392 405 374 353

153 252

331 I08

194

275

153

267

297

301

55

86

42

322

59

106

93

²⁷⁹

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Table XI 263.4 264 264.5 downstream Concentration Catalyst ^ temperature 289.5 292.8 293.3 NO N ^ O ⁰ C 235 10 % V _o 0 _K on aluminum «,« - "
^{2 5} oxide ²⁵⁶ ' ⁷ 2O3 237 I65 419 3 % Pt on aluminum- «-» / - _o
oxide ² ^ ⁰ ' ² 262.8 10 Ji ν _ο 0 _κ ^w " "265.6 131 404 3 Ji Pt "" 291.7 10 Ji V ₂ O ₅ "" ⁿ 294 143 449 3 £ pt ⁿ " 235 10 % V ₂ 0 ₅ on SiO ₂ -Al Example 3 455 0 10 # CuO "" 263.4 10 % V ₂ O ₅ "" 342 0 10 % CuO "" 289.5 10 % V ₂ O ₅ " ⁿ 91 0 10 Ji CuO "" Cr-activated iron _Ο , _{Λ o}
oxide ²⁵⁶ ' ² 534 0 Copper chromite It It 477 0 η It It 415 0 It 470 0 273 0 29 0 63 0 0 0 0 0 155 0 19th 0 0 0

The catalysts of Example 1 were subjected to a gas stream ₂ of 2% dimethyl sulfide, and 2% H in helium for 6 hours at 315.6 ⁰ C and then at the conditions of Example 1 without the addition of sulfur dioxide to Gasmisohung, which was passed through the reactors , checked. Essentially no formation of N ₂ O was observed for the base metal catalysts, the only one being

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Reaction product was Np and the downstream concentration of NO and N ₂ O was essentially the same as in Table XI. However, this pretreatment with dimethyl sulfide did not prevent NgO formation in the case of the platinum catalyst.

By pretreating the catalysts with the sulfur or selenium compounds, nitrogen oxide formation is prevented, whether or not sulfur dioxide is contained in the gas stream containing the nitrogen oxide. The invention eliminates the need to control the amount of SCU, which remains in the exhaust gas flow, for the reduction of nitrogen oxide without nitrogen oxide formation.

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Claims (1)

Claims SS = SS = S = S ====== (1.! Process for the catalytic reduction of nitrogen oxide by contacting a metal-based catalyst in the presence of ammonia and oxygen and reducing the Nitrogen oxide to nitrogen, characterized in that the one selected from the group consisting of copper, vanadium, Iron, chromium, nickel, molybdenum, cobalt, lanthanides and actinides or combinations thereof selected basic catalyst of a pretreatment by contacting with a Compound of the group selenium, sulfur and sulfur compounds is subjected to a nitrogen oxide, Oxygen and carbon dioxide-containing gas stream admixes ammonia and that the gas stream mixed with ammonia at Avoidance of the formation of nitric oxide in contact with is brought to the pretreated catalyst. 2. The method according to claim 1, characterized in that the basic catalyst made of the essentially copper, Vanadium and chromium oxides existing group is selected. J>. Process according to Claim 1 or 2, characterized in that the base catalyst is pretreated with a compound from the group consisting of sulfur, selenium, diethylsulphide, hydrogen sulphide, sulfur dioxide and cone sulphide. 4. The method according to claim 3, characterized in that the base catalyst is pretreated with a pretreatment gas stream of 2% dimethyl sulfide and 2 % hydrogen in helium. 709834/0967 ORIGINAL INSPECTED Λ. 5. The method according to claim 1, characterized in that ⁰ C and the contacting of the catalyst with the mixed gas stream at about 148.9 performs the pretreatment of the catalyst at about 204.4 to 482.2 bis 371 »1 ⁰ C. 6. The method according to claims 1,3 and 5, characterized in that one carries out the pre-treatment of the catalyst at 260 to 482.2 ⁰ C. 7. Process according to claim 6, characterized in that the catalyst is pretreated with a pretreatment gas stream of 2% dimethyl sulfide, 2 jtf hydrogen and helium. 8. The method according to claim 7, characterized in that the base catalyst is selected from the group consisting essentially of copper, vanadium and chromium oxides. 9. Process for the catalytic reduction of nitrogen oxide by contacting a metal oxide based catalyst in the presence of ammonia and oxygen, thereby characterized in that ammonia is added to a gas stream containing nitrogen oxide, oxygen and carbon dioxide, a certain amount of sulfur dioxide is added to the mixed gas flow and the gas flow is then in catalytic contact with the basic catalyst selected from the group of oxides of copper, vanadium, iron, chromium and molybdenum in avoiding the formation of nitric oxide. 10. A method for treating a base metal catalyst, characterized in that one of the substantially consisting of copper, vanadium, iron, chromium and molybdenum 709Ö3Ä / 0967 .3. Group selected Basismetallica ta Iy sat or contacted with a consisting essentially of sulfur * sulfur dioxide, dimethyl sulfide, carbon disulfide, hydrogen sulfide, and group the selected compound at a temperature between about 260 and 482.2 ⁰ C for the purpose of sulphidation of the catalyst. 11. The method according to claim 10, characterized in that that the catalyst consists essentially of copper, iron, chromium-activated iron oxide, vanadium and their Oxides existing group is chosen. 709834/0967